On 2022-10-25 03:15, Yang Yingliang wrote:
> Inject fault while loading module, kset_register() may fail.
> If it fails, the kset.kobj.name allocated by kobject_set_name()
> which must be called before a call to kset_register() may be
> leaked, since refcount of kobj was set in kset_init().
Technically, this is saying "If it fails, the kset.kobj.name may be leaked."
We want then to clarify that this is "allocated by kobj_set_name() which
must be called before a call to kset_register", so that needs to
be surrounded by commas (like a literary segue):
"If kset_register() fails, the kset.kobj.name allocated by kobject_set_name(),
which must be called before a call to kset_register(), may be
leaked."
I don't feel that the reason for the leak is "refcount of kobj was set in kset_init()".
It's a true statement, but not the reason for the leak--the reason for the leak is that
no one frees it on the error path.
> To mitigate this, we free the name in kset_register() when an
> error is encountered, i.e. when kset_register() returns an error.
>
> A kset may be embedded in a larger structure which may be dynamically
> allocated in callers, it needs to be freed in ktype.release() or error
"_by_ callers", since it's something they _do_: allocate.
> path in callers, in this case, we can not call kset_put() in kset_register(),
> or it will cause double free, so just call kfree_const() to free the
> name and set it to NULL to avoid accessing bad pointer in callers.
That's good.
> With this fix, the callers don't need care about freeing the name
> and may call kset_put() if kset_register() fails.
"don't need to care about freeing the name" --> "don't need to free the name"
> Suggested-by: Luben Tuikov <luben.tuikov@xxxxxxx>
> Signed-off-by: Yang Yingliang <yangyingliang@xxxxxxxxxx>
> ---
> v2 -> v3:
> Update commit message and comment of kset_register().
>
> v1 -> v2:
> Free name inside of kset_register() instead of calling kset_put()
> in drivers.
> ---
> lib/kobject.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/lib/kobject.c b/lib/kobject.c
> index a0b2dbfcfa23..3cd19b9ca5ab 100644
> --- a/lib/kobject.c
> +++ b/lib/kobject.c
> @@ -834,6 +834,9 @@ EXPORT_SYMBOL_GPL(kobj_sysfs_ops);
> /**
> * kset_register() - Initialize and add a kset.
> * @k: kset.
> + *
> + * NOTE: On error, the kset.kobj.name allocated by() kobj_set_name()
> + * is freed, it can not be used any more.
There's no need for "NOTE:"--it's just natural explanation of
what's happening, and what's expected in the doc comment to a function.
Drop it.
"is freed" is correct--that's a good change.
With these fixed, this patch is
Reviewed-by: <luben.tuikov@xxxxxxx>
Regards,
Luben
> */
> int kset_register(struct kset *k)
> {
> @@ -844,8 +847,12 @@ int kset_register(struct kset *k)
>
> kset_init(k);
> err = kobject_add_internal(&k->kobj);
> - if (err)
> + if (err) {
> + kfree_const(k->kobj.name);
> + /* Set it to NULL to avoid accessing bad pointer in callers. */
> + k->kobj.name = NULL;
> return err;
> + }
> kobject_uevent(&k->kobj, KOBJ_ADD);
> return 0;
> }
